Seattle filmmaker Lynn Shelton’s fourth feature is another agreeable exercise in small-scale humanism, an intimate three-hander set mostly in a vacation home in the San Juans. Mark Duplass is back from Humpday as an aging, grieving slacker, Jack, who has an ill-advised, drunken fling with Hannah (Rosemarie DeWitt), the visiting sister of his good friend Iris (Emily Blunt, deglammed with an earflapped ski cap), who arrives to find unexpected tensions in the cabin. In outline, Your Sister’s Sister could be a bed-hopping farce, but Shelton is less concerned with the sex than the emotional fallout. Hannah was recently dumped by her girlfriend. Jack’s dead brother once dated Iris, the high achiever in the bunch. As with Humpday and her prior My Effortless Brilliance, Shelton’s characters tend to be yearning and groping toward change in their lives: Jack seems harnessed by grief or bitterness; Hannah worries that she’s too old, that she’ll never have kids; and Iris has a secret to spill. Shelton lets her cast improvise on the three characters’ longing and confusion—resulting in meandering scenes without clever punch lines or clear end points. Instead, Shelton uses scenic island montage sequences for punctuation. Feelings take priority over words, and when her characters gush, they gush. (“I am emotionally, at best, precarious and at worst a cripple . . . “) Your Sister’s Sister is talky and naturalistic, with many moments of humor and truth—the latter often eloquently expressed with silence.